var data = [ 
	{"cluster" : "a", "attr1" : "3","attr2" : "5","attr3" : "4"},
	{"cluster" : "a", "attr1" : "2","attr2" : "4","attr3" : "5"},
	{"cluster" : "a", "attr1" : "4","attr2" : "3","attr3" : "6"},
	{"cluster" : "a", "attr1" : "6","attr2" : "2","attr3" : "3"},
	{"cluster" : "b", "attr1" : "3","attr2" : "2","attr3" : "3"},
	{"cluster" : "b", "attr1" : "4","attr2" : "3","attr3" : "2"},
	{"cluster" : "b", "attr1" : "2","attr2" : "4","attr3" : "4"},
	{"cluster" : "c", "attr1" : "4","attr2" : "5","attr3" : "5"},
	{"cluster" : "c", "attr1" : "6","attr2" : "6","attr3" : "6"},
	{"cluster" : "c", "attr1" : "2","attr2" : "5","attr3" : "2"},
	{"cluster" : "c", "attr1" : "4","attr2" : "4","attr3" : "4"},
	{"cluster" : "c", "attr1" : "5","attr2" : "3","attr3" : "2"}
	];